Sloped roofs are typically covered with mineral-surfaced asphalt shingles, such as those described in ASTM D225 (“Standard Specification for Asphalt Shingles (Organic Felt) Surfaced with Mineral Granules”) or D3462 (“Standard Specification for Asphalt Shingles Made From Glass Felt and Surfaced with Mineral Granules”), to provide a water-shedding function while adding an aesthetically pleasing appearance to the roofs.
Such asphalt shingles are normally made from asphalt-impregnated fabrics. The shingles also typically include colored roofing granules to provide aesthetically pleasing coloration to the shingles as well as to impart strength and durability to the shingles. The roofing granules are typically also used in asphalt-based roofing articles to help protect the asphalt from the effects of incident ultraviolet radiation.
It is known in the art, however, that conventional roofing materials, such as the described asphaltic shingles, reflect little near-infrared (“NIR” radiation; λ=about 700 nm to about 2500 nm) radiation and consequently absorb substantial solar heat. This absorption increases with dark-colored shingles; while white or lighter-colored asphalt shingles may have a solar reflectance in the range of about 25% to about 35%, dark-colored asphalt shingles may have a solar reflectance of only about 5 to about 15%. This comparatively high absorption of solar heat typically results in elevated temperatures in the environment surrounding the shingle.
This elevation in temperature in turn results in so-called heat-island effects that increase the need for energy-consuming cooling systems. The heat-island effects of the solar heat absorption of a dark-colored roofing article can be significant—temperatures as high as 77° C. have been observed on the surface of black roofing shingles on a sunny day having an ambient temperature of only about 21° C.
Several efforts have been made to address the issues raised by the described heat-island effects. Some efforts include incorporation of application of white- or light-colored pigments or coatings directly to roofing articles to enhance the articles' reflectivity. Consumers of roofing materials, however, have shown a marked aesthetic preference for black or dark-colored roofing articles.
Others have proposed roofing articles or granules having metal flakes, such as aluminum flakes, adhered to their surfaces, to provide a radiation-reflective surface. These approaches, however, impart reflectivity to the roofing article and result in articles that are not aesthetically pleasing to consumers.
Others have proposed the use of pigments dispersed in a polymer matrix to reflect NIR and reduce heat island effects. However, such use of pigments introduces aesthetically undesirable haze into the finished article due to light scattering.
Accordingly, there is an ongoing need in the field for improved roofing materials that possess desirable NIR reflectance characteristics while also presenting an aesthetically pleasing appearance. There is also a related need for processes capable of producing such improved roofing materials.